Photoabsorption of the Peroxide Linkage Defect in Silicate Glasses

The peroxide linkage (Si-O-O-Si) is a common defect in silicate and germanosilicate materials with local or global excess of oxygen. Possible routes for its formation include the rebonding in a silicon vacancy site, the reaction of a misplaced oxygen atom with a normal Si-O-Si linkage, and the trapping of an O sub 2 molecule in an oxygen vacancy. Some authors have suggested that the lowest excitation of the peroxide linkage defect is a 3.8 eV oxygen lone pair pn* ->po* transition. Other groups have assigned this transition at higher than 6eV. In this work, first-principles quantum chemical techniques on cluster models have been used to investigate the photoabsorption of the peroxide linkage defect in silicate glasses. The effects of geometry, basis sets, and cluster size have been considered carefully to derive converged values for the low-lying excitation energies.